1. Field of the Invention
This invention relates to dispersant additives for lubricating oils. More particularly, the invention relates to the modification of conventional polyamine dispersants so that they can be used in internal combustion engines which contain fluorohydrocarbon-type engine seals without causing discoloration, decomposition, and mechanical or dimensional degradation of the seals.
2. Description of the Prior Art
The deterioration of a lubricating oil during service in an internal combustion engine results in the formation of varnish-like deposits and the generation of products which agglomerate to form sludge-like materials. Since this varnish and sludge interferes with efficient engine operation, it has become conventional practice to incorporate into lubricating oils certain chemical compositions which have the ability to reduce or prevent the formation of sludge and the deposition of varnish. These additives are broadly referred to as dispersants.
Among the many types of dispersants which have been developed, polyamine dispersants are highly effective and are widely used. For the purpose of this application, a polyamine dispersant is an oil-soluble composition which contains at least one basic amine group and is effective as a dispersant additive for lubricating oils.
Fluorohydrocarbon elastomers are increasingly being used in fabricating the flexible seals which are used in internal combustion engines. These seals are used, for example, to prevent leakage of lubricants at the point where moving parts, such as a crankshaft, leave the engine. Any substantial leakage of lubricant from the engine is obviously undesirable.
Unfortunately, engine seals prepared from fluorohydrocarbon compositions are subject to discoloration and mechanical deterioration when used in engines which are lubricated with lubricating oils containing polyamine dispersants. The polyamine dispersants interact with the fluorohydrocarbon compositions of the seals, causing the seals to swell and to lose mechanical and dimensional integrity. The rate of attack of the fluorohydrocarbon compositions by a polyamine dispersant appears to be directly proportional to the concentration of polyamine dispersant and to the operating temperature of the engine. As the engine operating temperature rises, the rate of decomposition of the seal rises proportionately. As interaction of the dispersant with the seal continues, the mechanical strength and dimensional integrity of the seal increasingly deteriorates until the seal fails to prevent the leakage of lubricant from the engine.
U.S. Pat. No. 3,442,808 (Traise et al.) is directed to the preparation of a dispersant by reacting a polyalkenyl succinic anhydride with a Mannich condensation product prepared by condensing an alkyl-substituted phenol with formaldehyde and a polyalkylene polyamine. The polyalkenyl succinic anhydride is derived from the reaction of maleic anhydride with a polymer of a mono-olefin having three or four carbon atoms wherein the polymer has a viscosity at 210.degree. F. (99.degree. C.) of about 50 to about 10,000 Saybolt Universal Seconds. It is disclosed that reaction of the Mannich product with the polyalkenyl succinic anhydride results in a dispersant having improved oil solubility properties. However, this patent fails to suggest the reaction of a Mannich product with a low molecular weight substituted succinic anhydride for any purpose.
U.S. Pat. Nos. 3,639,242 (LeSuer) and 3,708,522 (LeSuer) are directed to the post-treatment of high molecular weight, oil-soluble, mono- and polycarboxylic acid esters with acylating agents to provide compositions which are useful as dispersants in lubricants and fuels. The esters are derived from aliphatic polyhydric alcohols and, among many others, amino alcohols are disclosed as being suitable. In addition, the acylating agents used for the post-treatment process are C.sub.1 -C.sub.30 mono- or polycarboxylic acids, their halides, anhydrides or mixtures thereof. However, these patents fail to either teach or suggest that polyamine dispersants cause the deterioration of fluorohydrocarbon compositions and fail to teach or suggest that such dispersants can be passivated toward fluorohydrocarbon compositions by reaction with specific amounts of a dicarboxylic acid or anhydride. Consequently, these patents offer no guidance with respect to the specific selection of polyamine dispersants and adjustment of the concentration of dicarboxylic acid or anhydride to achieve passivation of these dispersants toward fluorohydrocarbon compositions.